So many foods contain tryptophan that it's not even funny, anyway. PLUS, tryptophan will really only get absorbed in any appreciable amount in your brain if taken on an empty stomach.... and eating turkey kind of disqualifies that The amount you take in during thanksgiving is negligible.

It's totally the carb-crash and overstuffing yourself which makes you sleepy - a full stomach draws blood away from your brain and limbs and makes you drowsy.